Datenblatt-Suchmaschine für elektronische Bauteile |
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TC1267VET Datenblatt(PDF) 5 Page - Microchip Technology |
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TC1267VET Datenblatt(HTML) 5 Page - Microchip Technology |
5 / 14 page © 2002 Microchip Technology Inc. DS21378B-page 5 TC1267 4.0 THERMAL CONSIDERATIONS 4.1 Thermal Shutdown Integrated thermal protection circuitry shuts the regulator off when die temperature exceeds 160°C. The regulator remains off until the die temperature drops to approximately 150°C. 4.2 Power Dissipation The amount of power the regulator dissipates is primarily a function of input and output voltage, and output current. The following equation is used to calculate worst case actual power dissipation: EQUATION 4-1: The maximum allowable power dissipation (Equation 4-2) is a function of the maximum ambient temperature (TAMAX), the maximum allowable die temperature (TJMAX) and the thermal resistance from junction-to-air ( θJA). EQUATION 4-2: Table 4-1 shows various values of θJA for the TC1267 packages. TABLE 4-1: THERMAL RESISTANCE GUIDELINES FOR TC1267 IN 5-PIN DDPAK *Tab of device attached to topside copper. Equation 4-1 can be used in conjunction with Equation 4-2 to ensure regulator thermal operation is within limits. For example: Given: VINMAX =5V± 5% VOUTMIN = 3.217V ILOADMAX = 400mA TJMAX = 95°C TAMAX = 70°C θJA = 27°C/W (DDPAK mounted on 1000 sq mm topside copper area) Find: 1. Actual power dissipation 2. Maximum allowable dissipation Actual power dissipation: PD ≈ (VINMAX –VOUTMIN)ILOADMAX = (5.25V - 3.217V) 400mA =813mW Maximum allowable power dissipation: In this example, the TC1267 dissipates a maximum of 813mW; below the allowable limit of 926mW. Copper Area (Topside)* Copper Area (Backside) Board Area Thermal Resistance (θJA) 2500 sq mm 2500 sq mm 2500 sq mm 25°C/W 1000 sq mm 2500 sq mm 2500 sq mm 27°C/W 125 sq mm 2500 sq mm 2500 sq mm 35°C/W Where: PD ≈ (VINMAX –VOUTMIN)ILOADMAX PD VINMAX VOUTMIN ILOADMAX = Worst case actual power dissipation = Minimum regulator output voltage = Maximum output (load) current = Maximum voltage on VIN PDMAX =(TJMAX –TAMAX) θJA Where all terms are previously defined. PDMAX =(TJMAX –TAMAX) θJA = (95 – 70) 27 = 423mW |
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